I use the telnet command to check if MySQL port is responding.

telnet 3306

I use the ctrl character to disconnect. This is working as expected. How do I use this command in shell script?

  • Actually, do the echo with newlines as Janne propose, and add a sane timeout value with -w. – 3molo Aug 5 '11 at 9:34

If you're just looking to check if the port is open, try:

$ nc -zv 3306
Connection to localhost 3306 port [tcp/mysql] succeeded!

nc will return 0 if the port is open and 1 if it is not. This is quite helpful for scripting as well. Omit the v switch to keep it quiet:

if ! nc -z 3306
  • Thanks. But the -z switch is working on server but not working on another. Do I need to check the version of nc command? – shantanuo Aug 6 '11 at 4:41
  • Perhaps. What version is the one not working? – Cakemox Aug 6 '11 at 4:46
  • The -z switch is working correctly. I was wrong, ignore the above comment. – shantanuo Aug 7 '11 at 4:51

nc is much better for non-interactive usage. Try something like

echo -e "\n\n" | nc 3306
  • If I execute this, I get some garbled output, but the command doesn't exit. Does someone know why? – Christoph Wurm Aug 5 '11 at 18:09
  • Hmmm? It should exit. – Janne Pikkarainen Aug 6 '11 at 5:08

If you don't have nc, you can use bash special files redirectons:

head -1 < /dev/tcp/ >/dev/null && echo MySQL is on || echo MySQL is off

To automate telnet script, you should use expect. See the expect home page.


This is my script for any specific cases .

DATE=`date +%Y-%m-%d`
TIME=`date +%H%M%S`

for port in 80 25 22 443 110
if telnet -c $host $port </dev/null 2>&1 | grep -q Escape; then
  echo "$DATE $TIME  $port: Connected" >> $LOG_OK
  echo "$DATE $TIME $port : no connection" >> $LOG_FAIL



I would use netcat and it's '-w' instead;

host:~ user$  nc -w 1 3306
5.1.57-1~dotdeb.1?WO`rA*L#h?b4z.pmT;i~^;host:~ user$ 

Here is how to use telnet in bash shell/expect

# just do a chmod 755 one the script
# if you get "Escape character is '^]'" as the output it means got connected otherwise it has failed

set ip [lindex $argv 0]
set port [lindex $argv 1]

set timeout 5
spawn telnet $ip $port
expect "'^]'."

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